Chemiluminescence is defined as the reaction of two or more chemicals to create light. One class of chemiluminescence uses a mixture of hydrogen peroxide with an oxalate and a dye dissolved in a suitable solvent to generate light. Hydrogen peroxide reacts with the oxalate to produce an unstable strained ring, which releases energy that excites the dye. As the dye returns to its ground state, a photon of light is released. Hydrogen peroxide and oxalate are consumed in this reaction, whereas the dye is not. Commercially available glowsticks use this reaction and can produce light for over 6 hours in a wide variety of colors. The structure of the dye determines the wavelength of light emitted. Examples of dyes include 9,10-diphenylanthracene which creates blue light, or rhodamine B which emits red light. Recent advancements in glowstick chemistry involve extending the lifetime of the chemical reaction, increasing its brightness, or creating new colors. Literature describing modifications of chemistry include U.S. Pat. Nos. 3,691,085 (1972), 4,678,308 (1987) and 6,126,871 (2000), all of which are incorporated herein by reference.
An early report of a packaged chemiluminescent device is mentioned in U.S. Pat. No. 3,819,925 (1974) in which the reactive chemicals are kept separate by storing a solution of hydrogen peroxide in a glass vial, which itself is stored inside a plastic tube also filled with a solution of oxalate and dye. The chemiluminescent reaction is initiated when the glass vial is broken, combining the hydrogen peroxide with the other chemicals. Slight adaptations of this packaging scheme are described in U.S. Pat. Nos. 4,064,428 (1977) and 4,379,320 (1983). Another variation is presented in U.S. Pat. No. 5,121,302 (1992), in which the two liquid parts are stored in a plastic bag, separated by a barrier. Removing the barrier causes the chemicals to mix, resulting in the chemiluminescent reaction. These systems lack the ability to control the extent of the chemical reaction. That is, once the reaction is initiated, it cannot be reversed or altered, leading to consumption of all contents of the glowstick. Control of the luminescent parameters is predetermined by the packaging volume of the chemicals. This is a disadvantage that limits applications requiring a user-defined reaction volume.
U.S. Pat. No. 3,973,466 (1976) describes a modification of both the chemistry and packaging of the chemiluminescent material. In this patent, the reactant tetrakisdimethylaminoethylene (TMAE) is microencapsulated. Microencapsulation is a technique in which micron-sized droplets of liquid are surrounded by an impermeable solid shell wall. When TMAE is exposed to the atmosphere, it oxidizes and produces green light. In this case, the shell wall isolates the core reactant from the air, until the capsules are crushed. An advantage of this one-part chemiluminescent system is the ability to widely disperse the capsules over a large area for perimeter control. However, there are few choices for color and the reaction lifetime is limited to fifteen minutes. Interestingly, the patent briefly describes applying this concept further to the oxalate/hydrogen peroxide chemistry typically used with the glowsticks. In this illustration, microcapsules containing the dye, oxalate and solvent are mixed with another batch of microcapsules containing liquid hydrogen peroxide. This blend of capsules is crushed together, releasing the dissimilar cores and starting the chemiluminescent reaction. This arrangement has disadvantages since the two types of microcapsules need to be in intimate contact with each other for the reaction to proceed, an unlikely event when dispersed over a large area.
It is desirable to develop a true one-part microencapsulated chemiluminescent system based on the oxalate/hydrogen peroxide chemistry. This system would take advantage of the wide range of dyes available, as well as the long luminescent lifetimes of these systems. Additionally, this system would allow the user to portion the desired amount of reactants, reducing waste. Finally, this approach would allow the freedom to widely disperse the capsules.